1. Field of the Invention
This invention relates to an electromagnetic relay (EM relay), and, more particularly, to an EM relay suited for performing the large current-controlled switching operation.
2. Description of the Prior Art
Recent remarkable developments of integration techniques has greatly contributed to achieving a simplified structure of communication systems, control devices and home electrical appliances. This trend is similarly observed in automobiles having mechanically movable mechanisms controlled by electronic circuits.
Those systems, devices, appliances and the power supply circuits therefor are generally equipped with switching elements for large current-switching operations of from several to several tens of amperes. Almost all of the semiconductor switching elements currently available are, however, incapable of such switching operation with a large current, and are susceptible to failures by the application of an abnormal voltage and current caused by lightning bolts or current mixture. An EM relay is, therefore, indispensable to a mechanical switching element in order to effect the switching operation with high reliability under a large current application. However, the EM relay provided with mechanical switching contacts and an electromagnetic driving mechanism for driving such contacts is inevitably larger in size than a semiconductor switching element. This size becomes an obstacle to the recent trend toward the realization of more compact and lighter devices.
To meet such a trend, an EM relay which is light and small enough to be packaged on the same printed substrate with other electronic circuit components and which is adaptable to the large current-switching operation has been described in U.S. Pat. No. 4,535,311. However, this proposed relay cannot provide sufficient dielectric strength since a coil for exciting a core and lead-wire terminals of stationary contact members with electric contact elements are placed in close proximity.
Moreover, the switching operation at a large current generally tends to cause an arc discharge which, in turn, causes particles to be vaporaized from contact material to be deposited around electric contacts. Since such deposited particles are electrically conductive, they deteriorate the insulation to short-circuit contact circuits as the switching operation of the EM relay is repeated.